1. Field of Invention
The present invention relates generally to reflective film having a large plurality of extruded or coextruded layers, where the thickness of the layers varies non-linearly throughout the thickness of the film to produce a very broad band reflective film. Such films may be used to great advantage in an electro-optical glazing structure having reflection, semi-transparent, and transparent modes of operation which are electrically-switchable for use in dynamically controlling electromagnetic radiation flow in diverse applications.
2. Brief Description of the Prior Art
The use of multilayer polymer films for controlling reflectivity has been known for many years. Such films comprise many layers, generally alternating between two types of transparent polymer, each having different refractive indices and an appropriate thickness related to the wavelength of the light to be controlled. U.S. Pat. No. 3,711,176, by Alfrey, Jr. et al. details theoretical details of such a film. U.S. Pat. No. 3,610,729, by Howard Rogers introduces a multilayer polarizer, where each alternate layer is birefringent, where the index of refraction for light of a first linear polarization differs from layer to layer and that linear polarization is reflected, and the index of refraction for light of the second linear polarization is the same from layer to layer and the second linear polarization light is transmitted. The bandwidth of the light reflected from such multilayer films is generally limited to a small portion of the bandwidth of visible light (20 nanometers in the case of the Alfey patent. Also, if infra red reflecting film is required which is transparent in the visible region, higher order effects occur to produce unwanted reflected colors from the film. U.S. Pat. No. 5,103,337, by Schrenk et al. proposes using more than two different materials to control unwanted higher order effects. U.S. Pat. No. 5,686,979, by Weber et al., proposes to use multilayer reflecting polarizing film as a xe2x80x9csmart windowxe2x80x9d for the control of light by reflecting the light. The reflectivity, however, is generally limited to a narrow bandwidth and such films are not equally transparent outside of the reflective bandwidth of the films. General references on polymer dispersed liquid crystals may be found in detail in xe2x80x9cPolymer Dispersed Liquid crystal displaysxe2x80x9d, by J. W. Doane, a chapter in xe2x80x9cLiquid Crystalsxe2x80x9d, Ed. B. Bahadur, World Scientific Publishing, Singapore, and xe2x80x9cCLC/polymer dispersion for haze-free light shutters, by D. Yang et al. Appl. Phys. Lett. 60, 3102 (1992). Smart Window Design is treated in xe2x80x9cElectrochromism and smart window designxe2x80x9d, by C. Granqvist, Solid State Tonics 53-56 (1992) and xe2x80x9clarge scale electochromic devices for smart windows and absorbersxe2x80x9d, by T. Meisel and R. Baraun, SPIE 1728, 200 (1992). The above identified U.S. Patents. and references are hereby incorporated by reference.
It is an object of the invention to provide a reflective multilayer polymer film having a very wide bandwidth.
It is an object of the invention to provide a reflective multilayer polymer film having little variation in the reflectivity outside of the reflective bandwidth of the film.
It is an object of the invention to provide a polarizing reflective multilayer polymer film having a very wide bandwidth.
It is an object of the invention to provide a polarizing reflective multilayer polymer film having little variation in the reflectivity outside of the reflective bandwidth of the film.
It is an object of the invention to provide a xe2x80x9csmart windowxe2x80x9d using a polarizing reflective multilayer polymer film having a very wide bandwidth.
It is an object of the invention to provide a xe2x80x9csmart windowxe2x80x9d using a polarizing reflective film having a very wide bandwidth combined with a reflective multilayer polymer film having a very wide bandwidth.
It is an object of the invention to provide a xe2x80x9csmart windowxe2x80x9d using a polarizing reflective film having a very wide bandwidth combined with a reflective multilayer polymer film having little variation in the reflectivity outside of the reflective bandwidth of the film.
It is an object of the invention to provide a xe2x80x9csmart windowxe2x80x9d using a polarizing reflective multilayer polymer film having a very wide bandwidth combined with a light scattering layer for further control of transmitted light.
The present invention provides a reflective film comprising a large plurality of pairs layers of transparent polymer, each layer of the pair having a different index of refraction. The light reflected from the polymer interfaces add coherently to give high reflectivity. The layer thicknesses change through the thickness of the film in a substantially continuous and non-linear way, so that a very broad band width of light may be reflected and so that higher order effects are minimized.